Conventional nerve block needles are hollow straight needles for conducting local anesthetic solution into close proximity of the nerve to be blocked, i.e., anesthetized. Most peripheral nerves in the body are easily blocked with a straight needle because they are easily accessible, being unobscured by bony structures. The intercostal nerves are exceptions as they are inaccessible, being situated in a groove in the inside arcuate surface of the ribs, one nerve per rib. Furthermore lung tissue is situated millimeters away from the nerves at a deeper level. It is difficult to get close to the nerve to be blocked with a straight needle since it must clear the rib to get to the nerve area and injection then has to be made at a distance from the nerve. This risks failure of the block unless a large volume of anesthetic solution is used. Large volumes are dangerous if multiple nerves are to be blocked, as this risks a systemic toxic reaction from overdosage which may be fatal.
Additionally, lung tissue being situated millimeters away from the intercostal nerves, needle puncture of the lung causes air to leak outside the lung with subsequent collapse of the lung, the complication known as a pneumothorax. It is a potentially fatal condition if not recognized and appropriately treated. Diagnosis and treatment involves complexity and expense including diagnostic and subsequent chest X-rays, treatment procedures, prolonged hospitalization, and additional work for health care personnel.
It will thus be evident from the foregoing that the technique of intercostal nerve block requires much precision and skill. A method which increases the ease of performance and minimizes the risk has obvious advantages.
A known prior art method consists of pushing a straight needle through the skin directly onto the surface of the rib and then "walking" the needle off the lower edge of the rib in a number of short steps critically feeling for the step where the needle slips off the lower edge of the rib. When this critical event occurs, the needle is positioned underneath the rib, the depth of penetration being then determined by the skill and judgment of the operator. With the needle tip in ultimate position, injection of drug, i.e., local anesthetic into the nerve area by conventional syringe is performed. Whilst the complication of pneumothorax is admittedly rare, near misses are far more common. In an era of malpractice allegations and cost containment in medicine a potential for diminution or abolition of risk is obviously advantageous and not to be disregarded.